1. Field of the Invention
The present invention is broadly concerned with apparatus adapted to be mounted upon a vehicle equipped with an automatic transmission for the purpose of preventing shifting of the transmission between forward and reverse gears during movement of the vehicle, thereby eliminating transmission or drive train damage attendant upon such shifting while the vehicle is in motion. More particularly, the apparatus of the invention is preferably designed to operate in conjunction with the hydraulic braking system of the vehicle, i.e., means is provided for sensing essentially complete cessation of movement of the vehicle resulting from application of the brakes, and such sensing is used to release a shift locking mechanism and permit shifting of the transmission between forward and reverse gears.
2. Description of the Prior Art
Small tractors used in and around airports or similar facilities for hauling luggage wagons or other loads are typically provided with an automatic transmission which the operator can selectively shift between forward and reverse gears. A common occurrence with such vehicles is damage to the automatic transmission or drive train thereof, when the operator shifts between forward and reverse gears while the vehicle is moving. Additionally, damage to the tractor or tow bar can occur because of jackknifing of the tractor relative to the towed vehicles under these circumstances.
Passenger vehicles have in the past been provided with electrical interlock systems preventing shifting of an automatic transmission from park to a forward or reverse gear unless the brake pedal is depressed. This is intended to prevent unintended jerking or surging of the vehicle when put into a driving gear. However, these devices do not operate in a manner to prevent shifting of the transmission between forward and reverse gears while the vehicle is in motion.